clj-hash: clojure's hashes kind of brought to common lisp

clj-hash.lisp

(defmacro clj-hash (&rest kvs)
  "Destructures `kvs`: assums keys and values are paired together:

kvs ::= k1 v1 ... kn vn

Defines a sequence of functions ki that will obtain the value of ki
from a hash table.

Raises simple-error on ki not being a keyword.

Example:

CL-USER> (:quux (clj-hash :foo t :bar t :quux :steele))
:STEELE
T
CL-USER>

This idea is ported from Clojure's hash accessors."

  ;; Todo: remove unneeded gensyms, as well as determing the correct
  ;; management of length
  (let ((hash-table-sym (gensym))
        (kv-macro (gensym))
        (len (length kvs))
        (param-sym (gensym))
        ;;           may not need this
        (len-sym (gensym)))


    (loop for i from 0 below len by 2
       do
         (unless (eq (type-of (elt kvs i))
                  'keyword)
           (error "~a not a keyword" (elt kvs i) ))
         (when (fboundp (elt kvs i))
           (warn "~a already defined... redefining" (elt kvs i) )))
    (let ((function-list
           (loop for i from 0 below len by 2
              collect
                `(defun ,(elt kvs i) (,param-sym)
                   (gethash ,(elt kvs i) ,param-sym)))))

      `(let ((,hash-table-sym (make-hash-table))
             ;; quote kvs
             (,kv-macro  (list ,@kvs))
             (,len-sym ,len))
         (progn
           ,@function-list

           (loop for i from 0 below ,len-sym by 2
             do
               (setf (gethash (elt ,kv-macro i) ,hash-table-sym)
                     (elt ,kv-macro (1+ i)))))

         ,hash-table-sym))))